Generally, a stator of a motor is configured so that coils are respectively wound to form a plurality of layers around teeth portions, which are formed to protrude from corresponding yoke portions of stator cores in a radially inward direction of the motor. A large-sized stator core is used in a stator of a motor mounted on a vehicle, such as a hybrid vehicle and the like. The large-sized stator core, which is integrally formed, may cause a decrease of a yield rate of a material. Therefore, a splitable stator core is used, in which split cores are split at the yoke portions on the basis of each of the teeth portions. A stator having the splitable stator core is disclosed in the following.
According to JP2007-129835A, a stator core is configured with split cores, which are split at yoke portions in a direction crossing a circumferential direction of a motor. When the split cores are arranged so as to entirely form the annular shape, in split surfaces at which adjacent split cores contact each other, portions of the split surfaces in the vicinity of a rotor, rotated relative to an inner circumference of the stator core, contact each other preferentially. More specifically, in a state where the split cores are arranged so as to entirely form the annular shape, and where the split cores are integrally held, receiving pressure from an outer circumference of the stator core, the portions of split surfaces of the split cores in the vicinity of the rotor contact each other with a higher pressure than a pressure between other portions of the split surfaces being distant from the rotor. Further, the split cores are configured in a manner where a plurality of metal plates is layered. In general, considering assembly at the time of production, the metal plates are fixed to each other by dowel-fastening.
A position for dowel-fastening is set in the vicinity of an outer circumference of the yoke portions of the split cores, in order to reduce deterioration of motor performance. Due to the dowel-fastening, radially outer portions of the dowel-fastening portion of the split cores slightly expand in a radially outward direction of the motor. Further, when the stator core, in which the split cores are arranged so as to entirely form the annular shape, is press-fitted into a core holder, the dowel-fastening portions may expand because inner pressure occurs between the split cores in the circumferential direction of the motor. In a case where the stator core, having the expanded split cores, is press-fitted into the core holder, an outer circumferential portion of the stator core may contact the core holder partially because the dowel-fastening portions and the outer portions of the dowel fastening portions are expanded. As a result, a burr may occur and a holding force may decrease.
A need thus exists for a stator that is not susceptible to the drawback mentioned above.